The present invention relates to a push button switch having a springback force which is preferably used as an input key for electronic devices, such as wordprocessors, personal computers or the like. Furthermore, the present invention relates to a method for manufacturing the push button switches.
A conventional push button switch will be explained with reference to FIGS. 17 to 20. FIG. 17 is a plan view showing a conventional push button switch. FIG. 18 is a cross-sectional view showing the same. FIG. 19 is a perspective view showing an assembled condition of a link member used in the push button switch. FIG. 20 is a cross-sectional view showing an operating condition of the push button switch.
In the drawings, reference numeral 1 denotes a metallic base plate. Reference numeral 2 denotes a switch member comprising two films printed with a conductive paste. One film is put on the other film to constitute opposed switch contacts. Reference numeral 3 denotes a dome portion that is resiliently deformable. A protrusion 3A, used for pushing the opposed switch contacts of the switch member 2, is provided on a reverse surface of the dome portion 3. Reference numeral 4 denotes a resin casing having a central portion with a guide hole 4A for the dome portion 3 and both end portions with a pair of engaging recesses 4B.
Reference numeral 5 denotes a key top member having a cylindrical stem 5A at a central portion on a lower surface thereof and a pair of engaging portions 5B at respective end portions on the lower surface. The cylindrical stem 5A is slidably coupled with the guide hole 4A of the casing 4.
Reference numerals 6 and 7 denote a set of frame bodies being rectangular resin members as shown in FIG. 19. Each frame body has both ends with cylindrical fulcrum portions 6A and 6B1 (6B2), or 7A and 7B1 (7B2). Parallel arms 6C1 and 6C2 or 7C1 and 7C2 are connected at one end by the fulcrum portions 6A and 7A. Cylindrical axes 6D1 and 6D2 are provided at central portions of respective arms 6C1 and 6C2 of the frame body 6. Elongated holes 7D1 and 7D2 are opened at central portions of respective arms 7C1 and 7C2 of the other frame body 7. The cylindrical axes 6D1 and 6D2 of the frame body 6 are rotatably and slidably coupled with the elongated holes 7D1 and 7D2 of the frame body 7, respectively. The frame bodies 6 and 7, as a set, are assembled in an X shape when seen from a side. Thus, the frame bodies 6 and 7, when connected in a crossover fashion, cooperatively constitute a link member 8.
The fulcrum portions 6A and 7A provided at the lower ends of the link member 8 are held rotatably and slidably between the engaging recesses 4B provided at the both ends of the casing 4 and the switch member 2.
On the other hand, the upper fulcrum portions 6B1, 6B2 and 7B1, 7B2 are held rotatably and slidably in a pair of corresponding engaging portions 5B provided at the both ends of the key top member 5.
Next, operation of the above-described push button switch will be explained. When the key top member 5 is depressed downward by a finger placed on the upper surface of the key top member 5, the link member 8 held by the engaging portions 5B rotates about the cylindrical fulcrum portions 6B1, 6B2 and 7B1, 7B2. The lower fulcrum portions 6A and 7A, held rotatably and slidably between the casing 4 and the switch member 2, rotate and slide along the engaging recesses 4B in response to the downward movement of the key top member 5.
The movements of respective frame bodies 6 and 7 constituting the link member 8 are linked with each other by the engagement between the circular axes 6D1 and 6D2 provided at the central portions of the arms 6C1 and 6C2 and the elongated holes 7D1 and 7D2 opened at the central portions of the arms 7C1 and 7C2. When the key top member 5 is pushed, the key top member 5 is depressed downward substantially keeping a horizontal position. The dome portion 3 is collapsed or flattened by the key top member 5. The protrusion 3A pushes the switch member 2 so as to generate a predetermined turn-on signal.
Thereafter, the key top member 5 is released from a depressing force applied thereon. Upon releasing the depressing force, the dome portion 3 restores to its original shape by its springback force. Both the link member 8 and the key top member 5, pushed upward by the dome portion 3, return to their original positions shown in FIG. 18.
According to the above-described push button switch, the X-shaped link member 8 is interposed between the key top member 5 and the casing 4. The up-and-down movement of the key top member 5 is performed via the intervening link member 8. This provides ease in operation. However, the resin casing 4 has the guide hole 4A for holding the dome portion 3 in position and the engaging recess 4B for holding the link member 8. Thus, an overall height of the resin casing 4 becomes too high to realize a thin casing.
Furthermore, using many resin parts is not preferable in that the material cost is increased.